Is Mill's utilitarianism
consistent with the Harm Principle?[1]
Here's a passage that suggests that it is:

"A person may
cause evil to others not only by his actions but by his inaction, and in either
case he is justly accountable to them for the injury." (OL ch.1 ¶11; Cahn
p.932)

This suggests that a
government might be warranted in interfering with someone to make him do
something to help other people, e.g. turn over money to fund a welfare program.
If not turning over the cash harms people, then the government is justified in
making you turn it over! In fact, Mill lists a number of things that a
government may legitimately force someone to do, and one of those is
"saving a fellow creature's life":

There
are also many positive acts for the benefit of others which he may rightfully
be compelled to perform, such as to give evidence in a court of justice, to
bear his fair share in the common defense, or in any other joint work necessary
to the interest of the society of which he enjoys the protection, and to
perform certain acts of beneficence, such as saving a fellow creature's life or
interposing to protect the defenseless against ill usage--things which whenever
it is obviously a man's duty to do he may rightfully be made responsible to
society for not doing. (OL ch.1 ¶11; Cahn p.932)

By "harm,"
Mill means not only performing actions that result in bad consequences for
others, but also omitting actions and thereby failing to prevent bad
consequences from coming to others.

This broad concept of
harm definitely renders the HP consistent with Mill's utilitarianism -- but
does it also weaken the Harm Principle so much as to render it worthless?
E.g., by failing to join the Peace Corps and building bridges in Afghanistan,
you are omitting an action and thereby not preventing bad consequences from
affecting others. Does the HP thus allow the government to compel you to join
the Peace Corps?

Mill seems to have recognized
this threat to the HP, since he adds this caveat: compelling someone to
prevent harm to others "requires a much more cautious exercise of
compulsion than [compelling someone not to harm others]. To make anyone
answerable for doing evil to others is the rule; to make him answerable for not
preventing evil is, comparatively speaking, the exception."

Nonetheless, he believes
that "there are many cases clear enough and grave enough to justify that
exception." (OL ch.1 ¶11, Cahn pp.932-33)

[3.] Freedom of
Thought and Speech. (OL ch.1 and 2)

[3.1.] Personal
Freedoms.

Mill is concerned to
build "a strong barrier of moral conviction" (ch.1 ¶15, p.934)
against the encroaching restrictions on personal freedoms, both by the government
("legislation") and public opinion. To use Mill's own
famous phrase, he is concerned to insulate individuals from the tyranny of
the majority -- a tyranny which can operate both through political and
social institutions:

Like other tyrannies, the tyranny of the majority was
at first, and is still vulgarly, held in dread, chiefly as operating through
the acts of the public authorities. But reflecting persons perceived that when
society is itself the tyrant--society collectively over the separate
individuals who compose it--its means of tyrannizing are not restricted to the
acts which it may do by the hands of its political functionaries. Society can
and does execute its own mandates; and if it issues wrong mandates instead of
right, or any mandates at all in things with which it ought not to meddle, it
practices a social tyranny more formidable than any kinds of political
oppression, since, though not usualy upheld by such extreme penalties, it
leaves fewer means of escape, penetrating much more deeply into the details of
life, and enslaving the soul itself. (OL ch.1 ¶5, p.929)

Towards the end of ch.I
(¶12, p.933), Mill lists the following areas in which individuals should be
allowed freedom (by the government and by society as a whole):

2."tastes and pursuits" -- having whatever sort of life you
want, pursuing your own interests and activities (so long as you don't harm
others)

3."combination among individuals" -- i.e. freedom to associate
with whomever we wish

These three freedoms
are essential for a free society: "No society in which these liberties are
not, on the whole, respected is free, whatever may be its form of government;
and none is completely free in which they do not exist absolute and
unqualified." (ch.I ¶13, p.933)

Mill's argument in
favor of these freedoms seems to be utilitarian: "Mankind are
greater gainers by suffering each other to live as seems good to themselves
than by compelling each to live as seems good to the rest." (ch.I ¶13,
p.933)

[1]
Thomas (Mill, Oxford UP: 1985, p.96f.) writes about this and pulls an
unconvincing response out of OL ch.4.